1. Field of the Invention
The present invention relates generally to a laser beam machining apparatus and, more particularly, to a laser machining head of a laser beam machining apparatus provided with an easily replaceable nozzle as well as to a nozzle changer.
2. Description of the Background Art
There exist various types of conventionally known laser beam machining apparatuses used for machining (e.g., hot-cutting) a workpiece by use of laser light. In a floor-mount laser beam machining apparatus, for example, a nozzle through which assist gas is ejected against a work is provided on an optical axis of laser light at a lower part of a machining head. Being an element normally positioned close to a machining point, the nozzle is apt to collect debris (slag and dross) molten from the work, or even melt due to reflected laser light or the heat of adhering molten material of the work, during laser cutting operation. Different types of nozzles are used depending on the material and thickness of the work to be cut. Therefore, the nozzle is normally detachably fitted to the machining head for easy replacement in a laser beam machining apparatus. Typically, the laser beam machining apparatus is provided with a nozzle changing mechanism to facilitate nozzle replacement. As an example, Japanese Patent Application Publication No. 2004-98093 proposes a machining head combined with a nozzle which together constitute a built-in nozzle changing mechanism including a ball plunger for aligning axes of the machining head and the nozzle with each other and a ball plunger detent (positioning recess).
In the aforementioned conventional laser beam machining apparatus, the nozzle changing mechanism is configured to align the axis of the machining head with the axis of the nozzle by means of the ball plunger and the detent which mates with the ball plunger. In this nozzle changing mechanism, the ball plunger is located apart from the nozzle axis, and the mechanism does not include any arrangement for preventing the nozzle from turning around an axis of the ball plunger. Thus, the nozzle is left turnable around the ball plunger which is located apart from the nozzle axis. Consequently, there arises a problem that the nozzle can be replaced only with poor alignment of the axes of the machining head and the nozzle, or with poor concentricity thereof, and poor nozzle positioning reproducibility. A further problem which develops when the axes of the machining head and the nozzle are poorly aligned or when the nozzle is not positioned at an ideal distance form the work is that each cycle of nozzle replacement requires a nozzle alignment task to be done and a large amount of time for performing the task to accomplish high-quality machining.